It is known that ultraviolet ray having a wavelength of 200 nm to 360 nm not only takes a proliferating ability by acting on nucleic acid that is the protoplasm of bacteria to inhibit replication of DNA but also kills bacteria by destroying proteins, and other substances, that are formative substances of cytoplasm and cell membranes. An ultraviolet sterilizer that sterilizes air, or the like, by emit such ultraviolet ray is in actual use. The ultraviolet sterilizer is to sterilize microbes in the air by emit ultraviolet ray to influent air, and the like (see, for example, Patent Literature 1 and Patent Literature 2).
In the ultraviolet sterilizer of Patent Literature 1, in order for emit ultraviolet ray not to leak from a sterilizing chamber inside a casing that is a box, an upper portion of one of two facing sides in a sterilizing chamber is open as an air intake, a lower portion of the other one of the sides is open as an outlet opening, and air is caused to pass through the inside of the sterilizing chamber via these opening ports.
In the ultraviolet sterilizer of Patent Literature 2, to increase the irradiance of ultraviolet ray inside the sterilizer, reflectors are installed on wall surfaces inside a flow passage through which fluid flows, and ultraviolet ray is reflected multiple times by emitting ultraviolet ray obliquely to the reflectors. Thus, the ultraviolet sterilizer sterilizes fluid.